Gas generation and expulsion characteristics of Middle–Upper Triassic source rocks,eastern Kuqa Depression,Tarim Basin,China: implications for shale gas resource potential

Frontier exploration in the Kuqa Depression, western China, has identified the continuous tight-sand gas accumulation in the Lower Cretaceous and Lower Jurassic as a major unconventional gas pool. However, assessment of the shale gas resource in the Kuqa Depression is new. The shale succession in the Middle–Upper Triassic comprises the Taliqike Formation (T₃t), the Huangshanjie Formation (T₃h) and the middle–upper Karamay Formation (T_2–3k), with an average accumulated thickness of 260 m. The high-quality shale is dominated by type III kerogen with high maturity and an average original total organic carbon (TOC) of about 2.68 wt%. An improved hydrocarbon generation and expulsion model was applied to this self-contained source–reservoir system to reveal the gas generation and expulsion (intensity, efficiency and volume) characteristics of Middle–Upper Triassic source rocks. The maximum volume of shale gas in the source rocks was obtained by determining the difference between generation and expulsion volumes. The results indicate that source rocks reached the hydrocarbon expulsion threshold of 1.1% VR and the hydrocarbon generation and expulsion reached their peak at 1.0% VR and 1.28% VR, with the maximum rate of 56 mg HC/0.1% TOC and 62.8 mg HC/0.1% TOC, respectively. The volumes of gas generation and expulsion from Middle–Upper Triassic source rocks were 12.02 × 10¹² m³ and 5.98 × 10¹² m³, respectively, with the residual volume of 6.04 × 10¹² m³, giving an average gas expulsion efficiency of 44.38% and retention efficiency of 55.62%. Based on the gas generation and expulsion characteristics, the predicted shale gas potential volume is 6.04 × 10¹² m³, indicating a significant shale gas resource in the Middle–Upper Triassic in the eastern Kuqa Depression.     

川中地区上三叠统须家河组气源分析

通过对川中与川西北主要气田的天然气组分、天然气运移指标等资料的详细分析,发现川中地区须家河组天然气主要来自内部的次级生烃洼陷,其中须家河组二、四、六段气源分别为一、三、五段烃源岩,且不同含气层段之间很少有气源窜通的现象。最后指出即使生气强度小于20×108m3/km2,但只要紧邻生气洼陷,储层物性就相对较好,又有良好的构造背景,也能形成大中型气田。     

柴达木盆地侏罗系煤系烃源岩生烃潜力分类评价

柴达木盆地侏罗系发育泥岩、炭质泥岩、煤和油页岩等多种类型煤系烃源岩。受沉积环境控制,不同类型烃源岩之间有机质丰度、有机质类型及生排烃模式等差别很大。传统的评价方法低估了炭质泥岩和煤的生烃潜力。提出了基于单位岩石烃源岩产烃率的定量评价方法,对不同类型烃源岩的总生烃量和总资源量定量预测表明:炭质泥岩对侏罗系生烃总量和油气资源的贡献率分别达到44.8%和41.7%,整体提升了柴达木盆地侏罗系烃源岩的资源潜力,煤型气的资源潜力大幅度提高,对柴达木盆地天然气勘探具有重要指导意义。      

准噶尔盆地南缘侏罗系烃源岩排烃效率研究

准噶尔盆地南缘下部成藏组合勘探日趋重要,其主力烃源岩生烃潜力和排烃效率的研究亟待加强。根据排烃门限理论,利用生烃潜力法建立了准噶尔盆地南缘侏罗系烃源岩的生、排烃模式,并计算了烃源岩的生烃量、排烃量和排烃效率。研究表明,准噶尔盆地南缘侏罗系泥质烃源岩和煤层的排烃门限对应的镜质组反射率均为0. 7 %。侏罗系烃源岩的总生烃量为3 973. 84 x 108t,总排烃量为1 402. 71 x108t,其中八道湾组烃源岩排烃量占总排烃量的69.85%。准噶尔盆地南缘侏罗系烃源岩的平均排烃效率为35. 30%,不同层系不同岩性烃源岩,其排烃效率明显不同,泥质烃源岩排烃效率远大于煤层。综合分析认为,准噶尔盆地南缘侏罗系烃源岩生、排烃量大,排烃效率较高,下部成藏组合以侏罗系烃源岩为主力烃源岩,具有良好的资源潜力。     

Hydrocarbon generation and expulsion characteristics of Lower Permian P1f source rocks in the Fengcheng area,northwest margin,Junggar Basin,NW China: implications for tight oil accumulation potential assessment

Combined with the actual geological settings, tight oil is the oil that occurs in shale or tight reservoirs, which has permeability less than 1 mD and is interbedded with or close to shale, including tight dolomitic oil and shale oil. The Fengcheng area (FA), at the northwest margin of the Junggar Basin, northwest China, has made significant progress in the tight oil exploration of the Fengcheng (P₁f) Formation recently, which indicates that the tight oil resources have good exploration prospects. Whereas the lack of recognition of hydrocarbon generation and expulsion characteristics of Permian P₁f source rocks results in the misunderstanding of tight oil resource potential. Based on the comprehensive analysis of geological and geochemical characteristics of wells, seismic inversion, sedimentary facies, tectonic burial depth, etc., the characteristics of P₁f source rocks were investigated, and the horizontal distributions of the following aspects were predicted: the thickness of source rocks, abundance and type of organic matter. And on this basis, an improved hydrocarbon generation potential methodology together with basin simulation techniques was applied to unravel the petroleum generation and expulsion characteristics of P₁f source rocks in FA. Results show that the P₁f source rocks distribute widely (up to 2039 km²), are thick (up to 260 m), have high total organic content (TOC, ranging from 0.15 to 4 wt%), are dominated by type II kerogen and have entered into low mature–mature stage. The modeling results indicate that the source rocks reached hydrocarbon generation threshold and hydrocarbon expulsion threshold at 0.5% Ro and 0.85% Ro and the comprehensive hydrocarbon expulsion efficiency was about 46%. The amount of generation and expulsion from the P₁f source rocks was 31.85 × 10⁸ and 15.31 × 10⁸ t, respectively, with a residual amount of 16.54 × 10⁸ t within the source rocks. Volumetrically, the geological resource of shale oil is up to 15.65 × 10⁸ t. Small differences between the amounts calculated by the volumetric method compared with that by hydrocarbon generation potential methodology may be due to other oil accumulations present within interbedded sands associated with the oil shales. Copyright © 2015 John Wiley & Sons, Ltd.     

Critical conditions for natural gas charging and delineation of effective gas source rocks for tight sandstone reservoirs

Although it has been shown that the potential of tight‐sand gas resources is large, the research into the mechanisms of hydrocarbon charging of tight sandstone reservoirs has been relatively sparse. Researchers have found that there is a force balance during hydrocarbon charging, but discriminant models still have not been established. Based on the force balance conditions observed during gas migration from source rocks to tight sandstone reservoirs, a calculation formula was established. A formula for identifying effective source rocks was developed with the gas expulsion intensity as the discrimination parameter. The critical gas expulsion intensity under conditions of various burial depths, temperatures, and pressures can be obtained using the calculation formula. This method was applied in the Jurassic tight sandstone reservoirs of the eastern Kuqa Depression, Tarim Basin, and it was calculated that the critical expulsion intensity range from 6.05 × 10⁸ m³/km² to 10.07 × 10⁸ m³/km². The critical gas charging force first increases with depth and later decreases with greater depths. The distribution range of effective gas source rocks and total expelled gas volume can be determined based on this threshold. This method provides new insight into and method for predicting favourable tight‐sand gas‐bearing regions and estimating their resource potentials. Copyright © 2014 John Wiley & Sons, Ltd.     

北黄海盆地东部坳陷中生界烃源岩特征及其指示的油气勘探方向

为了量化表征北黄海盆地东部坳陷中生界主力烃源岩生、排烃特征,综合利用镜质体反射率(R_o)、残余有机碳含量(TOC)、岩石热解、干酪根镜检及饱和烃色谱等资料,在总结研究区烃源岩地化特征的基础上,通过油源对比明确主力烃源岩层并依托盆地模拟方法量化其生、排烃贡献.结果表明,北黄海盆地东部坳陷中生界的两类原油均来源于区内中侏罗统和上侏罗统两套主力烃源岩层,其中,中侏罗统烃源岩的有机质丰度整体处于"好-最好"级别,上侏罗统烃源岩的有机质丰度则以"中等-好"为主;二者均存在早白垩世末期和早中新世两次生、排烃高峰,但上侏罗统的排烃速率[q_e(max)=27.3×106 t/Ma]远高于中侏罗统的排烃速率[q_e(max)=4.2×106 t/Ma],对研究区油气成藏的贡献更大.虽然下白垩统暗色泥岩的生烃潜力有限,但其底部砂岩与紧邻上侏罗统主力烃源岩层构成的"下生上储"式的源储配置关系是区内最重要的勘探目的层,其次为中、上侏罗统内部"自生自储"式的有利成藏组合,同时,中侏罗统下部"上生下储"式的成藏组合也应予以重视.      

北黄海盆地东部坳陷勘探突破对我国近海残留“黑色侏罗系”油气勘探的启示

最新的勘探和研究证实,北黄海盆地东部坳陷发育了中、上侏罗统2套有效烃源岩并以上侏罗统为主力烃源岩层,在其供烃范围内形成了上侏罗统-下白垩统"下生上储式"和中-上侏罗统"自生自储式"2类成藏组合,取得了我国东部海域以侏罗系为唯一源岩的含油气盆地勘探突破。为进一步探索我国近海盆地残留"黑色侏罗系"的资源潜力和勘探前景,本文采用地震-地质综合解释、烃源岩地球化学分析、盆地模拟等方法,综合分析了我国近海主要盆地残留"黑色侏罗系"的分布和地球化学特征。结果表明,我国近海残留侏罗系暗色泥岩烃源岩非均质性较强,多属"中等"级别,局部发育"中等-好"、"中等-差"级别烃源岩,侏罗系烃源岩大多存在早（J₃-K₁）、晚（E₂末-N₁）2期生、排烃高峰,生烃总量达1.4×10¹¹ t,资源前景乐观,预测可形成侏罗系"自生自储式"和侏罗系-白垩系（或新生界）"下生上储式"2类源储组合。     

Geological and geochemical characteristics of the Middle–Lower Jurassic shales in the Kuqa Depression,Tarim Basin: an evaluation of shale gas resources

Middle–Lower Jurassic terrigenous shales constitute a set of significant hydrocarbon source rocks in the Kuqa Depression of the Tarim Basin. Until recently, however, most investigations regarding this set of hydrocarbon source rocks have mainly focused on conventional oil and gas reservoirs, and little research has been conducted on the formation conditions of shale gases. This research, which is based on core samples from nine wells in the Kuqa Depression, investigated the geological, geochemical, mineralogical and porosity characteristics of the shales, analysed the geological and geochemical conditions for the formation of shale gases, and evaluated the shale gas resource potential. The results show that the distribution of the Middle–Lower Jurassic shales is broad, with thicknesses reaching up to 300–500 km. The total organic carbon (TOC) content is relatively high, ranging from 0.2 to 13.5 wt% with a mean of 2.7 wt%. The remaining hydrocarbon generative potential is between 0.1 and 22.34 mg/g, with a large range of variation and a mean value of 3.98 mg/g. It is dominated by type III kerogen with the presence of minor type II₁ kerogen. The vitrinite reflectance values range from 0.517 to 1.572%, indicating the shales are in a mature or highly mature stage. The shales are mainly composed of quartz (19–76%), clay (18–68%) and plagioclase (1–10%) with mean contents of 50.36 wt%, 41.42 wt%, and 3.37 wt%, respectively. The pore spaces are completely dominated by primary porosity, secondary porosity and microfractures. The porosity is less than 10% and is mainly between 0.5 and 4%, and the permeability is generally less than 0.1 mD. These results classify the shale as a low-porosity and ultra-low-permeability reservoir. The porosity has no obvious correlation with the brittle or clay mineral contents, but it is significantly positively correlated with the TOC content. The maximum adsorbed gas content is between 0.82 and 8.52 m³/t with a mean of 3.37 m³/t. In general, the shale gas adsorption content increases with increasing the TOC content, especially when the TOC content is greater than 1.0%. The volumetric method, used to calculate the geological resources of the Middle–Lower Jurassic shales in the Kuqa Depression, shows that the geological resources of the Middle and Lower Jurassic shales reach 667.681 and 988.115 × 10⁹ m³, respectively with good conditions for the formation of shale gas and good prospects for shale gas exploration.     

松辽盆地双城-太平川地区烃源岩生烃潜力评价

双城-太平川地区为松辽盆地北部重要的油气勘探区域,通过对该区青1段、青2 3段、嫩1段和侏罗系暗色泥岩的有机质丰度和成熟度的综合分析,结果表明成熟的青1段泥岩是该地区最主要的烃源岩,青2 3段有局部的生烃贡献,嫩1段的生烃意义有限,侏罗系只能作为煤成气烃源岩。利用热演化程度参数推断出该区源岩的生烃模式和两个生烃高峰阶段。在此基础上,通过对不同构造单元的青1段泥岩生烃潜力与成熟度的综合评价,明确了该区3个有利的青1段生烃方位。     

Depositional environment,hydrocarbon generation and expulsion potential of the middle Permian Pingdiquan source rocks based on geochemical analyses in the eastern Junggar Basin,NW China

As the most important source rocks in the eastern Junggar Basin, the middle Permian Pingdiquan (P₂p) source rocks have attracted increasing attention after the discovery of tight oil in the Shazhang uplift. The P₂p source rocks are widely distributed (up to 7546 km²) and have an elevated thickness in the eastern Junggar Basin. To explore the P₂p tight oil resource in the eastern Junggar Basin, 113 core samples from 34 exploration wells were analysed geochemically and re-examined for their organic matter abundance, type and thermal maturity, hydrocarbon potential and sedimentary environment. Geochemical analysis results indicate that the P₂p source rocks are fair to good source rocks dominated by Type II kerogen, presently in a low mature–mature stage, and biomarkers and trace elements indicate deposition in a terrestrial to coastal environment under oxic to dysoxic, and fresh to brackish conditions, with possible intermittent seawater influence, implying proximity to the open sea. Based on hydrocarbon expulsion modelling, hydrocarbon expulsion began at 0.87% R_o, and the peak expulsion occurred at 1.1% R_o. Hydrocarbon generation intensities in the Shazhang uplift and the Wucaiwan sag are relatively large, with values centred at 4–6.5 million t/km² and 4–6 million t/km², respectively, with total hydrocarbon generation and expulsion from the P₂p source rocks approximately 4.56 × 10⁹ t and 1.44 × 10⁹ t, respectively, indicating significant tight oil exploration potential in the eastern Junggar Basin. The Shazhang uplift and the Wucaiwan sag are two hydrocarbon expulsion centres in the study area with the largest hydrocarbon expulsion intensity centred around the Shazhang uplift, exceeding 3 × 10⁶ t/km². We suggest that the area with high hydrocarbon expulsion intensities is a favourable target for tight oil accumulation and exploration.     

松辽盆地齐家—古龙凹陷中浅层烃源岩生烃量评价

随着近年来齐家—古龙凹陷中浅层烃源岩层段岩芯分析资料的积累和丰富,有必要再次对其烃源岩和生烃量开展评价.通过对齐家—古龙凹陷中浅层烃源岩岩芯样品的地球化学特征分析、测试结果进行统计,以低成熟度烃源岩样品的高温热模拟实验为基础,利用化学动力学方法计算齐家—古龙凹陷中浅层烃源岩成烃转化率随深度的变化规律,定量评价其生烃量.研究结果表明:齐家—古龙凹陷中浅层烃源岩有机质丰度高、类型好、处于未成熟至成熟的热演化阶段,生烃门限大约为1 500 m,约在1 750 m开始大量生烃;齐家—古龙凹陷青一段、青二三段和嫩一段烃源岩以生油为主,生油量分别为195.95×108 t、241.79×108 t和134.77×108 t,生气量分别为36.89×1011 m3、17.64×1011 m3和4.02×1011 m3,齐家—古龙凹陷中浅层油、气资源量分别为(28.63~57.25) ×108 t和(0.29~0.59) ×1011 m3.     

富有机质的黑色页岩和油页岩的有机岩石学特征与生、排烃意义

用近代有机岩石学与有机地球化学分析相结合的方法，对比研究了我国四川盆地等下古生界富有机质沉积的海相黑色页岩,和渤海湾盆地下第三系湖相油页岩的显微有机组成特征与热演化生烃、排烃作用的关系。观测分析结果表明:黑色页岩热演化程度很高，目前热解烃含量很低，但残余有机碳含量达1％～3％，黑色页岩中保存了早期生油阶段由无定型有机质生油作用转化而形成的微粒体有机质，和未排出的石油演变而来的残余沥青，表明其为原始生烃性能很好的烃源岩。根据黑色页岩中微粒体和残余沥青的含量，可用来了解已生—排烃量和再沉降埋深过程中古油藏储层沥青、微粒体和残余沥青再生气对古生界碳酸盐气藏的贡献。富有机质沉积的下第三系湖相油页岩热演化程度不高，游离烃（S1为0.2～1.4 mg/g）和热解烃（S2为8～44 mg/g），有机碳含量达2.4％～8％，是生油性能很好的烃源岩，油页岩中不仅存在强荧光的藻和无定型有机质，而且油页岩的纹层中广泛存在富有机质的荧光沥青，反映了有利于排烃运移的信息，表明是本区生油贡献最大的烃源岩。富有机质黑色页岩和油页岩的沉积结构构造特征、有机质的赋存形式、热演化中变化过程的对比观察结果表明:其生烃、排烃作用既有很多相似性，又有一定差别。     

从油气勘探的角度论博格达山的隆升

应用构造运动学、沉积原型恢复、有效烃源岩评价及改造型盆地模拟等技术和方法,综合研究分析了博格达山地区及周缘烃源岩特征与生排烃高峰期、构造-沉积演化、博格达山的隆升及其对油气勘探的意义。分析认为,现今博格达山地区及周缘在晚二叠世沉积期属于深湖-半深湖亚相,发育两套好-中等级别烃源岩,即上二叠统芦草沟和红雁池组,生、排烃高峰期属于侏罗纪末期-新生代;现今博格达山地区在侏罗纪末期开始隆起,与烃源岩生、排烃高峰期相同。博格达山隆升期,博格达山地区周缘柴窝堡凹陷与米泉地区尽管接受博格达山地区的供油量较少,但自身烃源岩厚度大,生烃能力强,具有较大的资源潜力,仍然是有利的油气勘探地区。     

烃浓度盖层封闭天然气的有效性及其研究意义

本文在烃浓度盖层封闭机理及其形成地质条件分析的基础上，通过烃浓度盖层封闭能力形成时期的确定，利用其与气源岩排气门限的匹配关系，探讨了烃浓度盖层封闭天然气的有效性。烃浓度盖层封闭能力形成时期只有早于或相近于气源岩排气门限时，才能有效地封闭气源岩排出呈分子扩散相运移的天然气；否则其封闭的有效性变差。并以松辽盆地三肇凹陷青山口组烃浓度盖层对下伏侏罗系气源岩天然气封闭的有效性为例进行分析，阐明其在天然气远景资源评价中的重要意义     

海拉尔盆地煤及煤系泥岩生排烃定量评价

海拉尔盆地具有多煤阶煤分布。煤系源岩生、排烃数据反映:最好的煤层是南上段,其次是大上段;最有利的煤系泥岩是铜钵庙组与南屯组。各凹陷煤系源岩生气量大小顺序为:呼和湖凹陷>贝尔凹陷>乌尔逊凹陷>呼伦湖凹陷。各凹陷煤系源岩生油量多少顺序为:乌尔逊凹陷>呼和湖凹陷>贝尔凹陷>呼伦湖凹陷。煤系源岩排油量大小顺序为:乌尔逊凹陷、贝尔凹陷、呼和湖凹陷、呼伦湖凹陷。可见,乌尔逊凹陷、贝尔凹陷、呼和湖凹陷具有良好的煤成油气勘探前景,是海拉尔盆地寻找煤成气、煤成油资源不可忽视的有利地区。      

柴达木盆地北缘侏罗系页岩气地质条件

侏罗系泥页岩是柴达木盆地的主力烃源岩之一,具备形成页岩油气的地质条件。对采自柴北缘鱼卡、大煤沟、小煤沟、开源、绿草沟、大头羊等煤矿附近地表露头的11块中侏罗统泥页岩样品进行单样品多参数实验分析,探讨了陆相页岩有机地化、储层物性、含气量等参数之间的关系,建立了页岩气资源评价参数体系。结果表明,柴达木盆地北缘中侏罗世处于浅湖-半深湖湖相沉积,断裂较发育,泥页岩富含有机质,具有低孔、低渗、低熟、较高含气量等特点,具备形成页岩油气的地质条件,进一步的勘查开发需优选地层压力系数高、保存条件较好、脆性矿物含量高的页岩气甜点区。     

煤系页岩气的基本特点与聚集规律

煤系页岩气是页岩气的重要类型之一。从煤系岩性组合、煤系页岩气地化特征和盖层条件等方面入手,剖析了煤系页岩气的生、排烃能力及保存条件,总结了中国煤系泥页岩的分布特征与发育规律。研究表明:煤系干酪根以腐殖型(III型)为主,H/C较低,总有机碳TOC值高;生烃母质的性质导致煤系泥页岩以生气为主,且具有长期缓慢生烃、排气态烃困难、滞后,排烃效率低、残留烃量大等特点;煤系中的煤层既是良好的气源岩,又对下伏层位的页岩气起到封盖作用,因此,煤系泥页岩具备较好的聚集成藏潜力。      

库车坳陷三叠-侏罗纪烃源岩生气特征与生气模式

根据热解实验和动力学模拟计算结果,研究了塔里木盆地库车坳陷侏罗纪煤、煤系泥岩及三叠纪泥岩的生气特征与生气模式。结果表明,库车坳陷三叠-侏罗纪烃源岩具有良好的生气性,尤其在进入中、高热演化阶段,甲烷产率更高,且侏罗纪煤和煤系泥岩的甲烷产率要高于三叠纪泥岩。侏罗纪和三叠纪烃源岩均以生气为主,是库车坳陷的有效气源岩,但前者的生气贡献明显高于后者。      

准噶尔盆地南缘侏罗系烃源岩评价

第三次资源评价(三次资评)结果表明准噶尔盆地侏罗系石油资源量占盆地总资源量的30%以上,天然气资源量占盆地总资源量的28%,其中30. 7%的原油资源和45. 7%的天然气资源分布在准噶尔盆地的南缘,可见应深人分析南缘侏罗系主力烃源岩的特征及其生烃潜力。通过对三次资评之后勘探所积累的地质地球化学数据的系统分析,认为准噶尔盆地南缘有机质类型总体以且II₂型和III型为主,纵向上发育了一套优质烃源岩(八道湾组)和两套中等丰度的烃源岩 (三工河组和西山窑组),烃源岩的规模远远大于三次资源评价的结果。这3套烃源岩均达到了成熟一过成熟的演化阶段,在白垩纪末期进入生油高峰期,在新近纪末期进入生气高峰期,生油气关键时刻与圈闭的形成和定型匹配良好,有利于形成大型和超大型油气藏。研究成果对指导准噶尔盆地南缘油气勘探具有重要的理论和实际意义。